Question

Electric quadrupole. Figure 22-41 shows an electric quadrupole.
It consists of two dipoles with dipole moments that are equal in
magnitude but opposite in direction. What is the value of E on the
axis of the quadrupole for a point P a distance z from its center
(assume z >> d)? Take Q = 2qd^2 (which is known as the
quadrupole moment of the charge distribution.)